In recent years, all-in-one notebook computers have come into widespread use. Computers of this type often includes a high-quality display and high-quality speakers to allow users to view movies with high picture quality or listen to music with high sound quality.
At the same time, portable music players which allow users, by means of headphones or earphones, to easily listen to music whenever they want without bothering others have also come into widespread use. It has also become customary to listen to music from such a player by connecting speakers to the player and listening through the speakers instead of through headphones or earphones.
Since high-performance speakers for connection to portable music players are expensive, users who own a notebook computer with high-performance speakers naturally desire to listen to music from the player by connecting the player to the notebook computer and using the speakers of the computer.
In a notebook computer including a volume knob, it is easy to control the volume of the music output from the speakers. Various processing methods concerning a control member such as a volume knob have been proposed in the prior art (for example, see Jpn. Pat. Appln. KOKAI Pub. No. 11-271041).
However, when the notebook computer is off, listening to music from a portable music player through the speakers of the computer is impossible. This is because recent notebook computers are configured such that software, in the form of an operating system (OS), performs all resource management including volume control. Therefore, in a notebook computer including a volume knob, a signal indicating the position of the knob is input to the OS, and volume control is performed under control of the OS. Consequently, when the computer is off, so that volume control by software is impossible, listening to music from a portable music player through the speakers of the computer is impossible. Thus, to listen to music, the user has to turn the computer on merely to use the speakers.
Jpn. Pat. Appln. KOKAI Pub. No. 11-271041 discloses a “position detection apparatus which does not need initial setting work to be performed when the power is turned on, has good linearity in the relationship between the detected position and the output signal, and can achieve high reliability and reduction in cost”, but does not address allowing the user to control volume on a personal computer configured such that, the OS performing all resource management, volume control by software is impossible when the computer is off.